I took a new early issue, 2 1/2" M-66 back in the 70's and had a four inch barrel installed. Had a sweet set of Farrant stocks on it (that I wish I STILL had) and ahd the acction worked over.

Great carry piece for that time. Ended up selling it and moving on to a Colt Commander in .45 acp. That carried a lot easier.

I have seen several RB, four inch guns over the years. I'd hazard a guess that the majority were reworks like mine.